The present invention relates to an embolization device for positioning in a blood vessel, comprising an elongated wire body which in its unloaded condition has a predetermined shape and has an elongated shape with a substantially straight center line during its insertion through a catheter to a placement site in the blood vessel and after its release from the catheter assumes a complexly curved shape which depends on the predetermined shape and on the blood vessel impact on the wire body, which wire body preferably has a coupling means at its back end.
Embolization devices in the form of coils where the wire body is formed by a thread extending helically around the center line of the wire body are well-known within radiology, where embolization coils are used for a number of different purposes all with the common feature that it is desired to limit or stop the free flow of blood in an area of a blood vessel. One example of an endovascular field of application for embolization devices for percutaneous, transluminal insertion using minimally invasive techniques, can be mentioned occlusion of an aneurism to prevent rupture of the vessel wall with resulting bleeding. Aneurisms may occur anywhere in the vascular system, but particularly cerebral and abdominal aneurisms require treatment to avoid life-threatening conditions. Another application is occlusion of arteriovenous malformations (AVM), where short-circuiting of arteries and veins looking like skeins of wool may occur, or occlusion of arteriovenous shunts or fistulas, which are major short-circuits between the artery side and the vein side in the vascular system with resulting heavy undesired blood flow. A fourth example of an application is blocking of the blood flow to a tumor, and a fifth, closure of traumatically conditioned blood flows owing to incised wounds or other bodily injuries or gastrointestinal bleeding.
Since embolization devices can be used in many different places in the vascular system and in vessels with very differing sizes, many different coils have been specially designed with various basic designs of the predetermined shape, and each basic design is usually made in a number of different sizes. To treat emergency patients, radiologists today have to stock a large number of different coils, and in the endovascular repair normally many coils are used which are inserted individually and are placed in a pile at the site of placement to be occluded. Considerable expertise is required to select the correct coil sizes for the relevant application, and the risk of unintended migration of a coil to other vessel sites owing to insufficient fitting within the vessel cannot be disregarded.
Conventionally, the predetermined shape of the embolization devices is made so that the wire body is helical with a helix diameter of the same size or slightly larger than the relevant vessel lumen, so that the wound wire body exerts an abutment pressure against the vessel wall. If the helix diameter is too large, the pressure against the vessel wall may become injuriously high, and if it is too small, the wire body can easily be released and drift away. Embolization coils with a regular helical shape or irregular coil shape are known from, for example, U.S. Pat. Nos. 4,994,069, 5,122,136, WO094/11051 and WO94/11051; SU-1777842-A1 discloses a coil with a single helix, WO95/25480 describes a spiral coil, DE-295 18 932-U1 a spherical coil, and WO96/18343 and U.S. Pat. No. 4,994,069 coils with a random matrix shape.
Before insertion of the embolization device, a catheter is placed transluminally in the vascular system having its distal catheter end at the site of placement, whereupon a guidewire mounted with the embolization device is pushed in through the catheter. When the wire body leaves the distal end of the catheter, it seeks to assume the predetermined shape. If the size and shape of the device are deemed suitable for the vessel geometry at the site of placement, the wire body is disconnected from the guidewire. A number of applicable types of coupling means in the back end of the guidewire with associated corresponding part on the guidewire are known, see for example EP-A-720 838 disclosing a screw thread, U.S. Pat. No. 5,217,484 disclosing a prehensile claw, WO94/06503 disclosing a pin connection, WO94/06502 disclosing a clamp connection, WO96/00104 disclosing a conical thread connection and EP-A 717 969 disclosing an inflatable holder.
The object of the present invention is to provide an embolization device which is applicable for a number of different vessel geometries and sizes and which at its placement in the vessel assumes a complexly curved shape which provides effective occlusion by means of the wire body itself. It is also desirable to achieve the occlusion with a smaller number of devices than is possible in the known art in order thus to reduce the risk of travel of a device away from the site of placement and to reduce the time spent on performing the occlusion.
In view of this the embolization device according to the invention is characterized in that the wire body in its predetermined or first or unloaded shape has at least one section located between its front and back ends in which the center line has substantially no curvature or such a small curvature that along a length of at least 20 mm it follows a helix-free path, and that the front end section of the wire body is adapted to be frictionally locked to the vessel wall at its discharge from the catheter, before said helix-free section has been discharged from the catheter. Of course, while the wire body is within the catheter, it is constrained in a generally linear shape.
The distal end of the catheter is usually located immediately at or at a short distance from the site of placement when the front end section of the wire body is discharged from the catheter as the wire body is pushed at its back end. During the discharging, the end section will approach and abut the vessel wall. At the continued discharge, the end section will arrange itself along the vessel wall over a length that causes the end section to frictionally lock with the vessel wall. Frictional locking in the present context means that the frictional forces between the distal end section and the vessel wall reach a magnitude at which the column loading from the free end of the wire body located between the catheter opening and the closest point of abutment with the vessel wall is unable to move the end section in relation to the vessel wall. As the helix-free section has a length of at least 20 mm, at least part of the section will still be inside the catheter when the end section becomes frictionally locked. At the subsequent release of the helix-free section, the free portion thereof will bend sideways away from the closest point of abutment with the vessel wall and seek towards an opposite area of the vessel wall, as seen in relation to the closest point of abutment, where a frictional locking will also occur. Then discharge of a further portion of the helix-free section of the catheter will lead to renewed bending of the wire body in a new direction, etc. The length of the helix-free section can be adapted to the vessel geometry at the site of placement to be occluded, a longer helix-free section for the same vessel geometry making the embolization device arrange itself with more portions of the wire across the vessel lumen, thereby making the occlusion denser, and a shorter helix-free section producing a more open occlusion, should this be desired.
The embolization device provides the considerable advantage that the helix-free section itself automatically adapts to the vessel geometry in question, and is fastened securely to it without any risk of unintended release from the site of placement. The various fields of application of the embolization device display different specific problems, for example that the wire body should only exert a relatively limited pressure on the vessel wall at placement in an aneurism where the vessel wall may be in danger of rupturing, but has to exert a substantially larger pressure on the vessel wall at placement in a vessel to be occluded for blocking of the blood supply to a tumor or an AVM, where the vessel wall is strong and the certainty against release of the wire body has to be high. All these different desired properties of the device can be taken into consideration by designing the wire body with a rigidity adapted to the desired application, a greater rigidity providing a heavier abutment pressure against the vessel wall.
The device according to the invention has the further advantage that the cavity in the vessel is crossed by the wire body suitably many times in different directions. The wire body has its own property of rigidity effectively counteracting recanalization at the site of occlusion, and the crossing wire portions also abut the vessel wall at each end of the crossing portions, which also contributes to the long-term stability of the occlusion. The placement is furthermore conducted in such an orderly manner that the risk of knotting or locking filtration of the wire body is extremely low. This provides the advantage that if desired the wire body can always be repositioned in the catheter by retraction of the proximal end of the member.
Preferably at its back end the wire body has a coupling means so that at insertion and placement the embolization device is mounted on the guidewire, thus rendering it possible directly to reposition the device in the catheter in case of problems in connection with the occlusion. It is also possible to manufacture the embolization device without any coupling means and to push out the device from the catheter by means of a stylet-shaped pusher.
In some applications the front end section may constitute a substantially rectilinear extension of the helix-free section, and at its distal extreme end the end section may be provided with a guide means, which may, for example, be umbrella-shaped. Alternatively the device in a preferred embodiment may be formed so that the helix-free section of the wire body extends to the front end section, which is curved at its front end, the center line of the section here turning at least 90xc2x0, preferably from 120xc2x0 to 320xc2x0, in relation to the course of the center line in the helix-free section when the wire body assumes its predetermined shape.
Firstly, the curved end section gives the wire body a soft and flexible front end with an extremely low risk of injuring the vessel wall when the front end meets it. This embodiment is therefore suitable for embolization of aneurisms. If, at the time of placement, the catheter end is positioned so that the pushing-out direction of the wire body is at right angles to the vessel wall in the aneurism, the vessel wall is touched by the curved front end which, owing to its curvature, is resiliently deformed without applying any risky pressure to the vessel wall, and at the same time the wire body is maneuvered: to the side to follow the vessel wall. If the pushing-out direction forms an oblique angle with the vessel wall, the curved end section results in a turn of the wire body so as to follow the curvature of the vessel wall.
Secondly, the curved end section is an integral part of the wire body, and transverse forces acting on the end section when it meets the vessel wall may therefore via the end section be partially transmitted to the section of the wire body located further behind, so that it is maneuvered to fit with the shape of the vessel wall before it has been advanced all the way to the vessel wall. For application in aneurisms, the center line in the front end of the wire body preferably turns through an angle ranging from 120xc2x0 to 320xc2x0. Keeping the angle below 320xc2x0 prevents the end section in the predetermined shape from forming a full helical line which may, after placement in the aneurism, exert a greater pressure against the vessel wall than the pressure of the helix-free section, which is determined by the rigidity of the wire, as mentioned above. The angle of at least 120xc2x0 provides great certainty that the end section will nestle up along the vessel wall in the advantageously atraumatical manner.
For applications in aneurisms, the embolization device may further advantageously be formed so that the back end section of the wire body with the coupling means is curved, the center line of the end section turning at least 120xc2x0, and preferably from 140xc2x0 to 340xc2x0 when the wire body assumes it predetermined shape. When the embolization device has been placed in the aneurism in the complexly curved shape, the curved back end section causes the coupling means to lie protected inside the cavity of the aneurism, surrounded by the wire portions crossing the cavity. With this location, the coupling means is prevented from sticking out through the access opening to the aneurism and from abutting the vessel wall of the aneurism. An angle smaller than 120xc2x0 or larger than 340xc2x0 in some cases entails the risk that the coupling means sticks out.
When the embolization device is intended for placement at sites where the vessel has a relatively large lumen and a suitably strong wall, for example in vessels with AVM, shunts or fistulas, the front end section of the wire body is preferably curved and forms several helices, suitably in the form of a spiral with a decreasing helix diameter towards the front end when the wire body assumes its predetermined shape. When the front end section is discharged through the catheter opening, it assumes the helical shape immediately outside the catheter opening and can thereby be frictionally locked to the vessel wall in a very well-defined position in the vessel. The catheter can then be slightly retracted so that the helix-free section has a suitable free length between the end section and the catheter opening, whereupon the whole wire body can be pushed out of the catheter so that it automatically adapts to the vessel geometry in the manner described above. If the distal helices have a small diameter, they will be placed centrally in the lumen of the vessel and here prevent the outward curving wire body portions from being pressed centrally through and out on the other side of the already placed distal end section. Thus, in addition to an accurate positioning, the embodiment also renders it possible to achieve a compactly placed device that only extends over a short vessel length.
In a particularly simple embodiment the helix-free section extends from the front to the back end sections. Thus, the whole wire body can have homogeneous properties except in the two end sections. Such an embolization device has a wide field of application. For special applications, the device may alternatively be designed so that between the front and the back end sections there are several helix-free sections with intermediate sections which may be helical and/or may produce breakpoints in the curvature of the wire body when it assumes its predetermined shape. With a single embolization device of this design it is possible to occlude two or more mutually separated places in a vessel, for example on both sides of a fistula. When the front section of the wire body is positioned at the first site in the vessel, and the front helix-free section(s) is/are placed, the catheter can be retracted in the vessel to a position at the desired second site of occlusion, whereupon an intermediate section of the wire body is placed and frictionally locked to the vessel, and finally the remainder of the device is placed. The sections of the wire body placed at individual sites of occlusion are mutually connected via a portion of the wire body, which prevents travel of the embolization device away from one occlusion site. Furthermore the insertion procedures for provision of two separate occlusions are considerably facilitated.
The wire body can be formed in different ways. One possibility is to use a single solid thread of wire which is bent in the end sections to the desired predetermined shape. In the front end section the wire may have a smaller diameter and be wound helically around the center line of the section to increase the flexibility of the wire body front end. Another possibility is to construct the wire body from several thin threads which are laid, woven or braided together into a body of a larger diameter than the thin threads. From the manufacture of ropes or wires it is known that the laying, weaving or braiding can be effected in a pattern that imparts resilient properties to the resulting wire body. Owing to the extremely small outer diameter of the threads, this method of manufacture is costly, however. A third and preferred possibility is to form the wire body from a thread that extends helically around the center line of the wire body. This design involves several advantages. From the manufacture of conventional embolization coils it is well-known to wind a thin thread around a mandrel in order to provide an embolization coil, and in terms of manufacturing it is an advantage to manufacture the wire body by this well-tried technique. For a specific desired rigidity (or rather flexibility) of the wire body, the wire body may be given a rather large diameter with a helically wound thread, which gives the radiologist a better possibility of seeing the wire body during its positioning in the vessel, because the larger diameter makes the wire body more radiopaque.
In a preferred embodiment, in the helix-free section the wire body has a spring constant which, measured on a 50 mm long portion of the wire body, is of at least c=P/exe2x89xa70.0008 N/mm, P being an axially acting applied force measured in N, and e being the change in length measured in mm, preferably of 0.0015 N/mmxe2x89xa6cxe2x89xa60.08 N/mm, suitably in the interval of 0.0008 N/mmxe2x89xa6cxe2x89xa60.2 N/mm. The preferred spring constant depends on the relevant application, on the method of insertion and on the intended pressure of the device against the vessel wall. If the spring constant becomes substantially lower than 0.0008 N/mm, the ability of the device to lock against the vessel wall will become poor. For application in aneurisms having a diameter of up to 6 mm, the spring constant preferably ranges from 0.0015 N/mm to 0.08 N/mm, and for applications where the vessel wall is stronger, the spring constant preferably ranges from 0.008 N/mm to 0.2 N/mm.